Low CD4/CD8 ratio in classical swine fever postnatalpersistent infection generated at 3 weeks after birth

Classical swine fever virus (CSFV) is one of the most important pathogens affectingswine. After infection with a moderate virulence strain at 8 hours after birth, CSFV isable to induce viral persistence. These animals may appear clinically healthy or showedunspecific clinical signs despite the permanent viremia and high viral shedding, inabsence of immune response to the virus. Given the role played by this infection in dis-ease control, we aimed to evaluate the capacity of CSFV to induce postnatal persistentinfection at 3 weeks after birth. Nine pigs were CSFV infected and sampled weekly dur-ing 6 weeks and viral, clinical, pathological and immunological tests were carried out.Also, the CD4/CD8 ratio was calculated with the purpose to relate this marker with theCSFV persistent infection. The IFN‐αresponse was detected mainly 1 week after infec-tion, being similar in all the infected animals. However, 44.4% of animals were CSFVpersistently infected, 33.3% died and 22.2% developed specific antibody response.Interestingly, in persistently infected pigs, the T‐CD8 population was increased, the T‐CD4 subset was decreased and lower CD4/CD8 ratios were detected. This is the firstreport of CSFV capacity to confer postnatal persistent infection in pigs infected at3 weeks after birth, an age in which the weaning could be carried out in some swineproduction systems. This type of infected animals shed high amounts of virus and aredifficult to evaluate from the clinical and anatomopathological point of view. Therefore,the detection of this type of infection and its elimination in endemic areas will be rele-vant for global CSF eradication. Finally, the low CD4/CD8 ratios found in persistentlyinfected animals may be implicated in maintaining high CSFV replication during persis-tence and further studies will be performed to decipher the role of these cells in CSFVimmunopathogenesis.